Flexible insulated ducts are formed of a wire reinforced core wrapped in a blanket of insulating material covered with a flexible sleeve. The core is formed of a continuous coil of wire, usually covered by a flexible plastic material. Methods and apparatus for forming such ducts are shown in U.S. Pat. Nos. 3,216,459 and 4,351,682 incorporated herein by reference.
A problem with many of the synthetic plastic materials used to form the core is that while they may have high stretch resistance (i.e. tensile strength), they often have very low tear resistance. That is, while these materials may have high tensile strength, if a tear or cut begins it can quickly migrate or spread until the entire core unravels. Thus, a tear once started may continue to spread until the entire reinforcing wire helix comes apart, rendering the insulated duct useless. It would be advantageous if such tears or cuts could be stopped from spreading. Small tears, if prevented from spreading, would have little effect on the efficiency or function of the insulated duct.
Therefore, it is one object of the present invention to provide a method of strengthening the wire reinforced core of insulated flexible duct.
Another object is to provide a method of applying a strong tape to the duct core to strengthen it.
Yet another method is to provide an apparatus for applying reinforcing tape along the longitudinal surface of a duct core.
Still another object is to provide an apparatus for applying strengthening tape simultaneously while testing the strength of material bonds in a flexible duct core.